Films are available on the American market which can be applied to the panes of a motor vehicle to shade said panes. The automobile owner can thus provide any shade for his vehicle panes. However, there are legal guidelines in the U.S. for the shading permitted on motor vehicle panes. To enable the police to maintain these guidelines, a device is required which can measure the shading of vehicle panes. For this purpose, the device must not require an external power source, must be lightweight and portable, and must be easy to use. In addition, the device must permit rapid reliable measurement without the policeman using the device having to get into the vehicle.
The devices known from the prior art are not suitable for this purpose. These devices require a separate light source which has a high energy consumption so that it requires an external power source. In addition, in these known devices, the pane must be located between the light source and the photoelectric element of the device so that the known devices are suitable only for measuring small samples. Finally, the attenuation of the transmitted light in the range of the spectrum that corresponds to the spectral sensitivity of the human eye is critical for the effect of the shading of the motor vehicle panes. Known devices measure an "objective" attenuation of the light in the pane while "subjective" attenuation for the human eye is important for measuring shading of the motor vehicle panes.